Cisterns adn Tunnels

A complex underground net of tunnels, wells and cisterns was parallel to the visible town development. These were used to drain and canalise underground water and to supply water. This water network is still operating thanks to the upkeep, until the building of the modern waterworks in 1925. During the 13th century many changes to the urban order create problems to water-supply. So new waterworks were built up and the old cistern in Piazza del Popolo was opened again. In 1829, L. Astancolle re-designs the historical centre, so many wells were discovered ( nowadays more than 500 are known) . They date back to different ages and they were linked to the tunnels. This system can be divided into two groups:
1. open-air tunnels
2. tunnels built in gallery
The first ones were created in the terracing areas during the filling up of the bank, so their drainage action avoids the strong pressure caused by water on the walls. The second ones were built in galleries digging at the stratum level, in order to channel water for the town.
In Roman times all the water-supply depend on twelve cisterns put under Piazza del Popolo and Palazzo dei Priori. They are made up of concrete except some partition walls. They are linked through arched doors put along the central axis, but they are not aligned in order to avoid streams. It is possible to see different building techniques because of the upkeep, made in different times. In 1994 other cisterns were discovered ( the so-called new cisterns) set under the tobacconist's shop in piazza del Popolo. It is supposed that water entered these rooms through a link with the tunnels. This link could be in unexplored rooms.